Field of the Invention
The present invention relates to a water heater and particularly to a water heater of a latent heat recovery type capable of heating water by recovering latent heat of combustion gas.
Description of the Background Art
In replacement of an already placed tank water heater with an instantaneous water heater, there are locations where an already placed exhaust pipe (a B vent) cannot be removed from a point of view of maintaining appearance of buildings.
At such a location, a water heater can be replaced by leaving the already placed exhaust pipe and inserting an exhaust tube (a flexible exhaust tube) in the exhaust pipe. The exhaust tube should be smaller in diameter, because the exhaust tube cannot be placed in the exhaust pipe if the exhaust tube has a large outer diameter. In order to maintain a stable combustion state even when the exhaust tube is decreased in diameter, an exhaust suction and combustion type should be adopted for a water heater.
Such a water heater of an exhaust suction and combustion type is disclosed, for example, in Japanese Patent Laying-Open No. 60-186617. In the water heater described in this publication, a heat exchanger for recovering sensible heat, a heat exchanger for recovering latent heat, and a fan are arranged in this order on a downstream side in a flow of combustion gas produced in a burner. Namely, in the water heater of this type, the fan is arranged downstream of the heat exchanger for recovering latent heat in the flow of combustion gas.
In the above-described water heater of an exhaust suction and combustion type, since the fan is arranged downstream of the heat exchanger for recovering latent heat, drainage water produced in the heat exchanger is to be suctioned up to the fan. Even if the suctioned drainage water is delivered by air-blowing force of the fan to the exhaust tube, that is, to downstream of the fan in the path of the flow of combustion gas, drainage water may undergo condensation inside the exhaust tube and flow back to the fan. Also, rainwater may flow into the fan from the downstream side of the fan. Thereby, drainage water (including rainwater) accumulates in the fan, which may cause a problem that the air-blowing force of the fan is deteriorated.